1. Field of the Invention
The present invention relates to a geared motor that has a motor arrangement and a speed reducing arrangement.
2. Description of Related Art
A geared motor, such as one recited in Japanese Unexamined Patent Publication No. 2002-106649 (corresponding to U.S. Pat. No. 6,481,306 B2), is used as a drive power source of, for example, a power window system. In the above geared motor, a rotational speed of a rotatable shaft of a motor arrangement is reduced by a worm wheel of a speed reducing arrangement and is then transmitted to an output gear to drive a window regulator, which lowers and raises a window glass.
In the structure for transmitting the rotation from the worm wheel to the output gear, the worm wheel is rotatably supported by a support shaft (a center shaft), which is secured to a gear housing, and a cushion rubber is received in a recess, which is formed in one side of the worm wheel. The output gear is rotatably supported by the support shaft, and a transmission plate is secured to a worm wheel side end of the output gear. The output gear is made of a metal material to achieve a required strength, and the transmission plate and the worm wheel are made of a resin material to reduce the weight. The transmission plate and the worm wheel are engaged in a rotational direction through the cushion rubber. That is, the worm wheel and the transmission plate (the output gear) are connected with each other to transmit the drive force therebetween through the cushion rubber, which absorbs the shocks.
The worm wheel side end of the transmission plate axially protrudes from the worm wheel side end surface of the output gear and has a seal retaining hole at the protruded portion of the worn wheel side end of the transmission plate. An inner diameter of the seal retaining hole is larger than an outer diameter of the support shaft. That is, an inner peripheral surface of the seal retaining hole, the worm wheel side end surface of the output gear and an outer peripheral surface of the support shaft define an annular receiving recess, which opens on the worm wheel side thereof. An O-ring is received in the annular receiving recess. Furthermore, an annular protrusion, which is received in the annular receiving recess, is formed in the worm wheel around the support shaft. In the assembled state of the speed reducing arrangement, the O-ring is received in the annular receiving recess, and the annular receiving recess is closed by the annular protrusion of the worm wheel.
In the geared motor of the power window system, the output gear is exposed to a region where water, such as rain water or car wash water, is likely applied. Thus, water droplets may adhere to the output gear. However, the O-ring is closely engaged with its surrounding components (i.e., the components located on its four sides). Thus, the water, which is applied between the output gear and the support shaft or between the output gear and the transmission plate is limited from moving further into the interior of the gear housing.
The output gear and the worm wheel are rotatably supported by the support shaft. Thus, grease is applied in the space between the output gear, the worm wheel and the support shaft to provide lubrication and to limit abrasion. In the middle of the assembling operation of the speed reducing arrangement, the grease is applied to the support shaft at a location around the O-ring after installation of the worm wheel and the O-ring to the support shaft. Thereafter, the output gear, to which the transmission plate is secured, is installed to the support shaft.
At this time, the grease remains in the receiving recess. However, when the applied amount of grease is excessively large, the excessive amount of grease has no place to move. Thus, the excessive amount of grease may possibly push the O-ring out of the receiving recess. In some cases, the O-ring is expanded radially outward by the pressure applied from the compressed grease, so that a portion of the expanded O-ring may possibly be pinched between the transmission plate and the worm wheel and may be kept installed in that pinched state. Then, the pinched portion of the O-ring may be cut to cause a trouble.
In contrast, when the applied amount of grease is made too small to limit the above trouble, the sufficient lubrication and the sufficient abrasion limitation cannot be achieved. Furthermore, the grease also functions as rust inhibitor. Thus, rust may be generated in the metal component, at which the sufficient amount of grease is not applied.
Thus, it is required to precisely control the applied amount of grease, thereby causing tedious assembling of the motor (specifically, the speed reducing arrangement) and an increase in the assembling costs.